Hand Tool Motor Thermal Control via Dynamic Switch-Off
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Solution Overview
Problem
Existing temperature monitoring systems in hand-held power tools, such as electric screwdrivers, often fail to accurately detect motor temperature changes, leading to premature or delayed shutdown, which can result in overheating and damage due to their non-linear characteristics and installation-related inaccuracies.
Innovation Solution
A control device dynamically adjusts the temperature switch-off limit based on the actual temperature gradient, using a comparison with stored curves and gradient values to correct the switch-off limit, ensuring timely shutdown and maximizing motor performance without overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PTC thermistor is used as a temperature sensor, then the motor can be switched off at a certain temperature to prevent overheating, but the resistance value increases extremely at a certain temperature making it impossible to measure exact temperatures and requiring empirical determination of the switch-off limit
Solution Approach 1:
The patent transitions from using a PTC thermistor with highly non-linear characteristics to an NTC thermistor with essentially linear temperature characteristics. This parameter change in the sensor type enables precise temperature measurement across the operating range while maintaining reliable overheating prevention through accurate temperature monitoring.
2Measurement precision
If an NTC thermistor is used as a temperature sensor, then the temperature characteristic is essentially linear enabling better temperature measurement, but if installed unfavorably the actual temperature values lag behind the actual motor temperature causing delayed shutdown and potential motor destruction
Solution Approach 1:
The patent implements dynamic adjustment of the temperature switch-off limit based on the actual temperature gradient (rate of change). When the temperature rises rapidly (high gradient), the system lowers the switch-off limit to ensure timely shutdown. This dynamic approach compensates for thermal lag in sensor response and prevents motor destruction even with unfavorable sensor installation.
Solution Approach 2:
The system continuously monitors the temperature gradient and uses this feedback to adjust the switch-off limit in real-time. The control device compares the actual temperature gradient with a maximum permissible gradient and dynamically modifies the switch-off temperature threshold, creating a closed-loop control system that ensures reliable motor protection.
3Device complexity
If a fixed temperature switch-off limit is used, then the control logic is simple, but the motor must be switched off too early reducing power output or cannot deliver maximum power risking overheating
Solution Approach 1:
The patent replaces the fixed temperature switch-off limit with a dynamic limit that adjusts based on the actual temperature gradient. This enables the motor to operate at maximum power under normal conditions while automatically reducing the switch-off threshold when rapid temperature rise is detected, optimizing both productivity and safety without excessive complexity.
Solution Approach 2:
The system changes the switch-off temperature parameter dynamically based on the temperature gradient condition. Instead of a single fixed value, the switch-off limit becomes a variable parameter that adapts to the thermal state of the motor, allowing maximum power delivery while preventing overheating.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise temperature monitoring, preventing overheating while maintaining high performance by adjusting the switch-off limit according to the motor's thermal dynamics, thus extending the tool's operational life and safety.
Implementation Method 1
Temperature-dependent resistors are usually used as sensors to determine the motor temperature. The usual sensors, in particular so-called PTC thermistors (PTC), have highly non-linear temperature-dependent characteristics.
Implementation Method 2
the control device changes the temperature switch-off limit value as a function of an actual gradient representing the respective gradient of a profile curve of the actual temperature values
Data Source
Figure 1~2b
Figure 3~4
Figure 5
AI summary
The hand tool machine (10) has a controlling unit (30) for controlling an electric motor according to temperature actual value. The electric motor is provided with a temperature independent sensor (35), particularly resistor (55). The control unit is formed for correcting temperature-switching-off critical values according to a course of the actual temperature values.